Index: generic/nsf.c
===================================================================
diff -u -rc64f818543a3e40ed1fafcc58c50324448b39266 -r3ed6440e2cbe7612bba89469b3c44c376d857338
--- generic/nsf.c	(.../nsf.c)	(revision c64f818543a3e40ed1fafcc58c50324448b39266)
+++ generic/nsf.c	(.../nsf.c)	(revision 3ed6440e2cbe7612bba89469b3c44c376d857338)
@@ -14207,31 +14207,24 @@
 
   } else { /* no unknown called, this is the built-in unknown handler */
     Tcl_Obj *tailMethodObj = NULL;
-    fprintf(stderr, "UNKNOWN objv[1] %s\n", ObjStr(objv[1]));
     if (objc > 1 && ((*methodName) == '-' || (unknownObj && objv[0] == unknownObj))) {
       int length;
+      tailMethodObj = objv[1];
       if (Tcl_ListObjLength(interp, objv[1], &length) == TCL_OK) {
         if (length > 1) {
           Tcl_ListObjIndex(interp, objv[1], length - 1, &tailMethodObj);
-        } else {
-          tailMethodObj = objv[1];
-        }
-      } else {
-        /* The first ("method") argument to unknown is an invalid list, yet a valid message */
-        fprintf(stderr, "UNKNOWN2 objv[1] %s\n", ObjStr(objv[1]));
-        tailMethodObj = objv[1];
+        } 
       }
     }
-    fprintf(stderr, "tail %s MethodName(tail) %s\n", ObjStr(tailMethodObj), MethodName(tailMethodObj));
     result = NsfPrintError(interp, "%s: unable to dispatch method '%s'",
                            ObjectName_(object), (tailMethodObj != NULL) ? MethodName(tailMethodObj) : methodName);
   }
-
+  
   /*
    * Reset interp state, unknown has been fired.
    */
   rst->unknown = 0;
-
+  
   return result;
 }
 
Index: tests/methods.test
===================================================================
diff -u -r3c1482d9e1f80f0216250f5debade5d8edb1b17e -r3ed6440e2cbe7612bba89469b3c44c376d857338
--- tests/methods.test	(.../methods.test)	(revision 3c1482d9e1f80f0216250f5debade5d8edb1b17e)
+++ tests/methods.test	(.../methods.test)	(revision 3ed6440e2cbe7612bba89469b3c44c376d857338)
@@ -230,6 +230,60 @@
   ? {o eval :foo} "::o: unable to dispatch method 'foo'" 
 }
 
+nx::test case colon-unknown {
+  set o [nx::Object new {
+    :object method foo {a b c args} { return [current method]-ok }
+
+    ## Expansion to valid method calls (messages)
+    :object method expand-non-empty-list-1 {} {
+      {*}[list :foo 1 2 3 4 5 6];
+    }
+    :object method expand-non-empty-list-2 {} {
+      : {*}[list foo 1 2 3 4 5 6];
+    }
+    :object method expand-self-call-1 {} {
+      {*}[list :];
+    }
+    :object method expand-self-call-2 {} {
+      : {*}[list];
+    }
+
+    ## (Non-)expansion & unknown
+    :object method expand-unknown-1 {} {
+      :{*}[list foo 1 2 3 4 5 6]; # no expansion, yielding invalid list as method name
+    }
+    :object method expand-unknown-2 {} {
+      :{*}[list]; # no expansion, yielding invalid list as method name
+    }
+    :object method expand-unknown-3 {} {
+      :{*}; # no expansion, yielding invalid list as method name
+    }
+    :object method expand-unknown-4 {} {
+      :{*}{}; # no expansion, yielding invalid list as method name
+    }
+    :object method expand-unknown-5 {} {
+      :{\}}; # yet another invalid list (no expansion op)
+    }
+  }]
+
+  ? [list $o expand-non-empty-list-1] "foo-ok"
+  ? [list $o expand-non-empty-list-2] "foo-ok"
+  ? [list $o expand-self-call-1] $o
+  ? [list $o expand-self-call-2] $o
+
+  #
+  # Keep unknown messages compatible with Tcl's 'invalid command'
+  # messages in the cases below, e.g.: 
+  #
+  # proc =foo {args} {;}; ={*}[list foo 1 2 3 4 5 6]
+  #
+  ? [list $o expand-unknown-1] "$o: unable to dispatch method '{*}foo 1 2 3 4 5 6'"
+  ? [list $o expand-unknown-2] "$o: unable to dispatch method '{*}'"
+  ? [list $o expand-unknown-3] "$o: unable to dispatch method '{*}'"
+  ? [list $o expand-unknown-4] "$o: unable to dispatch method '{*}{}'"
+  ? [list $o expand-unknown-5] "$o: unable to dispatch method '{\}}'"
+}
+
 nx::test case mixinguards {
   # define a Class C and mixin class M
   nx::Class create C